As concerns for the environment increase and the need for better fuel economy is required, the use of alternate fuels in a vehicle is becoming more desirable. Liquified petroleum gas, or LPG may be used in more or less standard gasoline-type engines equipped with special fuel systems. LPG is made up of certain light hydrocarbon molecules. Therefore, LPG is a fuel that is liquid only under pressure. When the pressure on LPG is reduced, it vaporizes. Typical LPG fuels used for automotive engines include propane and butane. Because butane boils and turns to vapor at approximately 32.degree. F. (0.degree. C.) at atmospheric pressure, butane generally cannot be used in regions where temperatures fall below 32.degree. F. because the butane does not vaporize adequately. On the other hand, propane boils at -44.degree. F. (-42.2.degree. C.) at atmospheric pressure and therefore will vaporize at air temperatures in which the vehicle operates. Although LPG fuel includes some disadvantages such as greater cost of transporting and storing LPG because of special handling requiring pressurized tanks, its advantages are beginning to outweigh the disadvantages and especially for use in fleet operations.
It is known from tests using LPG fuel made on a number of transit companies on their fleet vehicles that LPG fuel offers many advantages. Some advantages using LPG fuel over conventional gasoline fuel include that LPG has a high octane number which allows for compression ratios in the engine over 10:1 which results in increased engine power output. Further, because LPG quickly vaporizes, little or no engine deposit is left in the cylinders. In addition, the LPG fuel cannot wash down the cylinder walls and remove lubricant therefrom. Therefore, cylinder wall, piston and piston ring wear is decreased which reduces engine wear, increases engine life, and keeps maintenance costs low.
Although LPG fuel may require a special pressurized fuel tank in the automobile to maintain the fuel in liquid form, many of the components traditionally used in a gasoline fuel injection system may be continued to be used when using LPG fuel. In the fuel delivery system of internal combustion engines, it is customary to connect electronically controlled fuel injectors to a fuel rail. The injectors deliver fuel to the engine in metered pulses which are timed to control the amount of fuel delivered and to coordinate the delivery with the operation of the engine. Because it is more difficult to meter the LPG fuel into the injectors when the fuel is in gaseous state, it is desirable to maintain the LPG fuel in the liquid state in the fuel rail. After a hot soak condition or during certain driving conditions it is difficult to keep the LPG fuel in the fuel rail in a liquid form. It is the intent of the present invention to address this concern.